Heat-treating of gear teeth



emma a aim UNITED STATES PATENT OFFICE HEAT-TREATING OF GEAR. TEETH Francis S. Denneen, Cleveland, and William C. Dunn, Shaker Heights, Ohio, asaignors to The Ohio Crankshaft Company, Cleveland, Ohio, a

corporation of Ohio Application March 23, 1942, Serial No. 435,912

(Cl. 26H) 4 Claims.

face zones of gears and similar articles.

In the heat treatment of metals generally and in the hardening of ferrous metals in particular, there have been no teachings which would enable those skilled in the art to produce hardened zones of metal of predetermined characteristics as to depth and general contour on articles having abrupt or irregular changes in surface form by the use of electric heat. Surface hardening processes used heretofore were not adapted to the hardening of such surfaces as the contacting surfaces of gear teeth or splines, the side walls of sliding keys and keyways, the rifled interiors of gun bores, and many other similar surfaces. In the hardening of such surfaces as those above enumerated, it is often important that adjacent surfaces as well as the core or metal under the surface, be kept softer in order that it be sufficiently ductile to resist fractures due to shock, vibrations and other causes. For instance, in a gear tooth, the addendum surfaces should be hard in order to resist the abrasion of sliding and rolling contact of other tooth surfaces, while the metal in the dedendum and at the root of the tooth which does not contact with any wearing or abrasive element, but which is submitted to heavy bending stresses due to the cantilever construction of gear teeth, should remain strong and comparatively ductile to prevent breakage or the formation of incipient fractures. Experience has taught that brittleness in steel usually increases with hardness, and the greater the brittleness the more the metaiis susceptible to the formation of surface cracks or incipient fractures which eventually extend far enough into the metal to cause complete failure of the section affected.

Our method and apparatus is applicable not the wearing surfaces of a gear may be hardened without detrimental changes affecting other parts of the gear. Another object is to provide a method and apparatus whereby the addendum portions of all teeth may be hardened simultaneously and uniformly. A further object is to provide a method whereby a portion of a gear after being hardened may be temperated to any desired degree. A still further object is to provide a method and apparatus whereby internal teeth or splines may be hardened simultaneously with the hardening of external teeth on the same gears. Numerous other objects will become apparent from the following description in which details of apparatus capable of producing improved results will be defined and new and advantageous steps in the procedure for obtaining such results will be described or suggested to those skilled in the art of heat treating.

Fig. 1 is a longitudinal section of oneform of our apparatus taken on line |-I of Fig. 2.

Fig. 2 is a fragmentary transverse section taken on line 22 of Fig. 1.

Fig. 3 is a fragmentary longitudinal section of a further modification of our apparatus taken only to gears, but to numerous other articles as hereinafter explained, such as splined shafts, reamers, drills, gun bores, the wearing surface of pulverizing and crushing machines, friction feed rolls and the like, and to almost any metal article requiring a hardened zone, particularly where there is an uneven surface.

With the aforementioned conditions in view, this invention then has as its chief object the provision of an apparatus and method where y substantially on line 3-3 of Fig. 4.

Fig. 4 is a fragmentary section taken at 44 of Fig. 3.

Fig. 5 shows the moving and control mechanism employed with the apparatus of Figs. 1 and 2.

Fig. 6 is a view substantially as indicated at 6- of Fig. 5.

Fig. 7 'is a view of the inductor as indicated at 1-1 of Fig. 4.

Referring now to Figs. 1 and 2, we show one form of apparatus for accomplishing the results of our invention. In this apparatus the gear 35 is secured on an arbor 36 which is geared by gears 31 and 38 to the tube 39 onto which inductor bars are assembled. Locking means such as a spring actuated plunger 40 is provided for holding the gear in such position as to bring one of the inductor bars, as 40, into central position in the space. between two adjacent teeth, as H and 42. With the inductor bar 40 in the position shown, high frequency current is caused to flow in this bar which induces currents of suflicient density in the adjacent surface zones of the teeth 4| and If to bring these zones to hardening temperature. Upon attaining this temperature, a quenching fluid is projected from the tube 39 through passages 43 in an insulating spider l4 and other passages It in the inductor bar, onto the heated surface of the teeth. A non-rotatable open side tube 46 inserted in tube 38 prevents the quench from flowing into passages other than the ones leading to the heated tooth surfaces or to adjacent regions.

After one pair of tooth faces has thus been hardened, the gear 35 is rotated which, through the gearing above mentioned, rotates the group of inductor bars so as to bring the next bar, as 41 for instance, into the adjacent tooth space 48 in which position the group of inductors is locked by spring operated plunger 40 wedgingly engaging the space between two inductors until the hardening cycle for this position has been completed. By means of contacts made at the opposite ends of the inductor bar by brushes 50 and when this bar is in heating position, the flow of current is restricted to that inductor bar much like the distribution of current in a commutator of a D. C. motor.

It will be evident that with a limited source of power and when the gear teeth are large, it may be possible to heat only one tooth face at a time instead of two opposite faces as above provided. To accomplish this the inductor may be so formed and positioned as to be brought into close proximity with one tooth surface only, it being spaced far enough from the surface of the opposite tooth to prevent injurious heating therein.

In the form of apparatus shown in Figs. 3 and 4 the gear I I0, the teeth of which are to be hardened, is carried on bushing III which is brought into driving engagement with the end of shaft II2 by means of screw I I3. Shaft I I2 is rotatably supported in frame II 4 of the apparatus and is rotated by gear I I5 mounted thereon. A rotatable inductor is supported on and rotated with tubular shaft II! which turns on stationary tube IIB to bring axial elements such as II9, I20 and I2I of the inductor into heating relation with the surfaces of successive teeth of gear IIO. Gear I I0 and the inductor are caused to rotate simultaneously and in correct relation with each other by gear I22 attached to tubular shaft II'I meshing with gear I I5.

The inductor comprises a copper ring I25 to which a cylindrical group of axially extending inductor elements such as II9, I20 and I2I are securely attached. These elements are molded in insulating material such as I26 to form a rigid cylindrical assembly with the inductor elements projecting radially like the teeth-of a gear and having their sides shaped to so conform with the faces of theteeth of gear IIO as to be brought into current inducing spaced relation with them. Current is delivered to the proper inductor elements from conductor rods I28 and I29 attached to a source of suitable inducing current. Two brushes located side by side and spaced to engage adjacent inductor elements 'as shown at I30 and I30. These brushes are held in engagement with the radial disc-like surface comprising the ends of the inductor elements and the insulation I26 interposed between these elements and carry the current from the conductor rods to the inductor elements, springs such as I3I holding the brushes in contact with the ends of the inductors. The brushes are thus brought into current conducting engagement with the ends of the elements so that current flows from rod I 28 thru one element such as I20 then across thru ring I25 to an adjacent element such as I 2| and then back to rod I29 which is shown in Fig. 7. There being no contact with any other element such as I I9 no current will flow in such other element until the inductor is turned. It will be observed that current flows in opposite directions in elements I20 and I2I to heat the sides of tooth I35. When the inductor and gear IIO are rotated an amount corresponding to one tooth space, elements H9 and I20 will move into current conducting contact with brushes I and I30 corresponding to the positions formerly occupied by elements I20 and I2I respectively and tooth I36 will enter the space between them corresponding to that occupied by tooth I35.

In this form of the apparatus the gears are indexed by a pawl and ratchet mechanism similar to that shown in Figs. 5 and 6 hereinafter de scribed. Shaft I38 is motor driven at a sufficiently slow speed to provide proper timing. Cam I39 operates pawl I40 to rotate ratchet disc I4I which turns shaft II! to move the inductor one gear space at a time. The heating and quenching are timed by drum or other timing device such as I42. Relay I43 operates the heating current connecting switch I44 and relay I45 operates the quenching fluid supply valve I41.

Quenching fluid is delivered thru tubular shaft I I8 which has a port I49 so located as to deliver the quenching fluid thru only passages such as I50 and I5I which lead immediately adjacent to as shown or thru only the inductor elements such as I20 and I2I which are in heating positions relative to the gear tooth such as I35. Passages such as I52 in tubular shaft I I! serve with port I49 as a distributor to limit the flow of quenching fluid to the correct inductor element passages.

It will be obvious that the apparatus above described comprises inductor members which automatically are brought into heating relation with surfaces of gear teeth as the gear is progressively rotated or indexed by steps, usually one tooth at a time. However, by multiplying the number of inductors and properly forming them several teeth can be hardened at each indexed location.

Figs. 5 and 6 show a diagram of the electrical connections and related means for controlling timed heating and quenching when the apparatus similar to that of Figs. 1 and 2 is employed. In this timer, discs I and I6I are carried by shaft I62 which shaft is driven by coupling I63.

Pawl comprising members I64 and I64 carried by an eccentric or cam I65 advances gear 38 one or more teeth at a time to rotate gear 35 the correct amount to bring an inductor member such as 45 into correct relation with two teeth of this gear. A brush contact I66 on disc I60 usually by a relay controls switch I61 in the circuit supplying current to terminals I60 and I69 of the inductor unit and brush contact I10 controls valve III for delivering fluid to tubular shaft 46 for quenching the teeth of the gear,

Other forms may be employed embodying thefeatures of our invention instead of the one herein explained, change being made as regards the means and the steps herein disclosed, provided the elements stated by any of the following claims or the equivalent of such stated elements be employed, whether produced by our preferred method or by others embodying steps equivalent to those stated in the following claims.

We therefore particularly point out and distinctly claim as our invention:

1. In apparatus of the class described for heat treating teeth of a gear, means for supporting the gear to rotate on an axis, an axially supported rotatable inductor of generally cylindrical form, said inductor comprising a plurality of conductor bars, the said bars lying generally along elements of the cylinder and projecting substanor the gear, and means 101 supplying inducing current to the bars when the bars have entered corresponding tooth spaces to induce heating current in faces of teeth adjacent to the bars.

2. In apparatus of the class described for heat treating teeth or a gear, means for supporting the gear to rotate on an axis, an axially m ported rotatable inductor of generally hollow cylindrical form, a cylindrical wall of said inductor comprising a plurality of conductor bars. the said bars lying generally along elements oi the cylinder and projecting substantially radially from the cylinderin spaced relation substantially like the teeth of the gear, insulating means separating the bars from each other along elements 0! the cylinder, gearing connecting the inductor and the gear supporting means to rotate the inductor in timed relation with the gear to bring successive inductor bars into successive tooth spaces of the gear, the said bars being adapted to enter said tooth spaces in closely spaced relation with races of the teeth or the gear, means for supplying inducing current to the bars when the bars have entered corresponding tooth spaces to induce heating current in surface zones oi the tooth faces, fluid delivery passages through the cylindrical wall 01' the inductor, and means associated with the axial support of the inductor for delivering fluid to the fluid delivery passages from said support to cool the inductor bars and quench the surface zones of the gear teeth, said last named means comprising a rotatable tubular shalt having ports for delivering the fluid to the passages through the inductor wall, and a substantially fixed tubular supporting shaft, the supporting shaft having a port through a wall thereof, said port being disposed to register with successive ports of the rotatable shaft to selectively deliver the fluid to those passages through the'inductor wall which lie adjacent to the tooth oi the gear being heated, a wall oi the said flxed shaft serving to exclude fluid from other pauages through the inductor wall to conflne quenching to those parts of the gear which it is desired to quench.

3. In apparatus of the class described ior heat treating teeth of a gear, means for supporting the gear to rotate on an axis, a rotatable inductor axially supported on a tubular shaft, th inductor comprising an insulating hollow cylindrical wall. a plurality oi inductor bars, said bars being supported by said cylindrical wall and projecting substantially radially therefrom in spaced relation substantially like the teeth of the gear, gearing connecting the inductor and the gearsupportingmeanstorotatetheinductorin,

timed relation with the gear to bring successive inductor bars into successive tooth spaces oi the gear, the bars being adapted to enter the tooth spaces in closely spaced relation with races of the teeth 01' the gear, means for supplying inducing current to the bars when the bars have entered corresponding tooth spaces to induce heatingcurrentinsuriacezcnesoithe tooth faces, fluid delivery pamages through the cylindrical wall oi the inductor, and means associated with the axial support 01 the inductor for delivering fluid to the fluid delivery passages of the inductor to cool the inductor bars and to quench the surface zones 0! the gear teeth; said last named means comprising the substantially flxed tubular shaft axially supporting the inductor, the tubular shaft having a port through a wallthereoi'. said ort being disposed to register with successive fluid delivery passages through the wall or the inductor to selectively deliver the fluid to those passages through the inductor wall which lie adjacent to the tooth oi the gear being heated, apartorthewalloithetubularshaitservingto exclude fluid from other passages through the inductor walltoconfln'equenchingtothoseparts oi the gear which it is desired to quench.

4. In apparatus or the class described !or heat treating spaced projections on a substantially cylindrical article, means for supporting the article to rotate on an axis, a rotatable heater axially supported to rotate on a substantially as fixed tubular shaft, the heater comprising a plurality of heating members, the said members having parts projecting from the heater in spaced relation substantially like teeth of a gear, gearing connecting the heater and the article sup- 40 porting means torotate the heaterintimed relation with the article to bring successive heater members into heating proximity with successive projections to heat surface zones or the projec tions, fluid delivery es through a part of the heater, and means associated with-the axial support of the heater for delivering fluid to the fluid delivery passages oithe heater to cool parts or the heater and to quench the surface zones o! the projections, said last named means comprising a substantially flxed tubular shalt axially supporting the heater, the tubular shaft having a port through a wall thereof, said port being disposed to register with successive fluid delivery passages through the heater to selectively deliver the fluid-to those passages through the heater which lie adjacent to the projection being heated, a part or the wall of the tubular shalt being adapted to serve to exclud fluid irom other passages through the heater to conflne quenching to those parts oi the article which it is desired to cool.

FRANCIS B. DENNEEN.

WILLIAM C. DUNN.

V I Certificate of Correction Patent N0 2,398,085. April 9, 1946.

FRANCIS S. DENNEEN ET AL.

It is hereb certified that errors appear in the above numbered patent requiring correction as f0 lows: In the drawings the present sheet 2 should be canceled and the 3 sheets of drawings, containing 7 figures as shown below, should be substituted for the 4 sheets now appearing as part of the Letters Patent:

A911] 19M5- F. s. DENNEEN ETAL 2,393,085

BEAT TREATING or GEAR} TEETH Filed March 23, 1942 3Shaets-Sheet l April 1946- F. s. DENNEEN ET AL 2,393,085

HEAT TREATING OF GEAR TEETH Filed March 23, 1942 3 Sheets-Sheet 2 INVENTORS HEAT TREATING OF GEAR TEETH Filed March 23, 1942 5 Sheets-Sheet 5 and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed thie 3rd day of September, A. D. 1946.

LESLIE FRAZER, First Assistant Commissioner of Patents. 

